1. Field of the Invention
This invention concerns the improvement of an ophthalmic photographic apparatus such as a fundus camera for photographing the fundus of a subject's eye using a fluorescent agent.
2. Description of the Prior Art
An ophthalmic photographic apparatus is well known in the prior art wherein the method of use consists of intraveneously injecting the fluorescent agent fluorescein, illuminating a fundus of a subject's eye with light in the visible wavelength region to cause the fluorescent agent to fluoresce, and photographing the fundus by means of the fluorescence emitted by the fluorescent agent.
In recent years, a fundus camera has been developed wherein the method of use consists of intravenously injecting the fluorescent agent indocyanin green, illuminating the fundus by light in the infra-red region to cause the fluorescent agent to fluoresce, and photographing the fundus. In this fundus camera wherein the method of use consists of illuminating the fundus by light in the infra-red region, an exciter filter which transmits only infra-red light in a specific wavelength range that causes the fluorescent agent to fluoresce is inserted in the illuminating optical system when the photograph is taken. And a barrier filter is inserted in a photographic optical system when the photograph is taken.
In order to cause the fluorescent agent to fluoresce by illuminating the fundus with infra-red light, however, an intense illumination is required. If there should thus happen to be a flaw or deterioration of the exciter filter provided in the illuminating optical system, not only infra-red light in the specific wavelength range but also light in other wavelength ranges reaches the fundus, and may cause damage to the retina of the subject's eye. Further, if there should happen to be a flaw or deterioration of the barrier filter which is provided in the photographic optical system, infra-red light in the specific wavelength range passes through the barrier filter in addition to the fluorescence of the fluorescent agent so as to form an image. The photographic image is therefore blurred, and a good photograph cannot be obtained.